The present invention relates to a high-pressure hydraulic pump, in particular an internal combustion engine radial-piston fuel pump.
As is known, in internal combustion engines, in particular diesel engines, such a pump operates at high pressure, even as high as 1,600 bars, and comprises a group of radial cylinders in which slide respective pistons activated by a common cam. Each piston has a return spring so as to move elastically during the fuel intake stroke, and is associated with an intake valve comprising a shutter which is normally kept closed by another return spring for opening the valve when overcome by the intake fuel pressure.
In one known three-radial-piston pump, each shutter has a plate cooperating with a corresponding seat in the cylinder, and is opened when the intake fuel pressure reaches roughly 5 bars; and the reaction of the three pistons on the drive shaft is normally balanced sufficiently by the 120xc2x0 spacing of the pistons.
In known radial-piston pumps, the shutter return spring is unaffected by the piston position. When the pump works at low capacity, e.g. below 30% of maximum, both the drive shaft and the delivery pressure of the various cylinders are subject to unbalance. In fact, the intake valves open with a variable amount of delay, and some may even not open at all, so that the pistons compress different amounts of fuel.
It is an object of the present invention to provide a highly straightforward, reliable high-pressure hydraulic pump designed to eliminate the aforementioned drawbacks typically associated with known pumps.
According to the present invention, there is provided a high-pressure hydraulic pump comprising at least one cylinder in which slides a piston, and actuating means for moving said piston positively in a compression direction; said piston being moved elastically in an intake direction opposite to said compression direction; and an intake valve comprising a shutter being fitted to said cylinder; characterized in that elastic means are provided between said piston and said shutter to push said shutter into a closed position by exerting elastic force varying with the position of said piston in said cylinder, so as to advance opening and closing of said intake valve.
More specifically, in a pump in which the shutter comprises a plate cooperating with a seat carried by the cylinder, and the plate is movable parallel to the piston, the elastic means comprise a helical compression spring located between the plate and the piston.